1. Field of the Invention
This invention generally relates to Braille display systems which are used to display stored alphanumeric text in a Braille code and, more specifically, it relates to Braille display systems which incorporate a mechanical Braille display and encode the characters of the alphanumeric text as three-dimensional Braille symbols consisting of multiple frames of information.
2. Description of the Prior Art
Through the use of Braille code, people with serious visual impairments are able to read text by touch. The Braille code consists of a list of different embossed symbols, each one corresponding to a specific alphanumeric character. The embossed symbols conform to a standardized format consisting of a three by two array of dot positions. Each dot position within the array is in one of two states, either "on" or "off", depending upon the presence or absence of a raised dot. By sensing the pattern of raised dots through touch, the visually impaired person can identify the symbol and thus, the character to which it corresponds. Using this approach, the visually impaired person can tactilely read alphanumeric text which has been translated into Braille by scanning the lines of embossed symbols with his fingers.
Originally, Braille code was developed for print media. Today, however, the media for Braille have expanded to include computer display terminals as well. Special Braille display terminals are available which make it possible for visually impaired people to read text stored in a computer. The Braille display terminals convert stored computer text into Braille symbols which then appear on a mechanical Braille display. Generally, the display is a string or window of electromechanical Braille display cells. Each cell contains an array of movable pins which can be raised or lowered within the cell to create any desired pattern of raised dots on the top surface of the cell. The visually impaired person tactilely reads the Braille symbols appearing on the display. And by electronically moving the window about the stored text, the user can read the entire text.
Since Braille code was originally developed for print media, however, it proves to be not well suited for displaying the computer-stored text of today. To be well suited, the Braille display terminal should be able to "show" the visually impaired person what the sighted user sees on the screen. Unfortunately, Braille codes found in the prior art have severely limited capacity They are adequate for encoding the limited information found in text which appears on the printed page, but they are not adequate for encoding computer-stored text which may be specially highlighted and formatted for visual display.
Since the standard Braille 3.times.2 array contains six dot positions, it can only provide 64 different symbols. Yet, for computer displays there are significantly more than 64 characters which must be encoded. Besides the 26 lower case alphabetic characters, there are 26 upper case characters and ten numeric characters, a total of 62 characters. Add to this list all punctuation marks and such commonly used characters as =,+, -, / (, ), $, and *, and the number already exceeds 64. Indeed, it may be desirable to represent all of the characters of the seven bit ASCII code, which is an accepted standard for computer based systems. The ASCII code contains 128 characters, requiring twice the capacity of the standard six-dot-position Braille code.
Text formatted for video display presents even greater challenges to Braille display systems. The video displayed text may contain video attributes or enhancements which convey essential information. For example, the available video attributes include double height or double width text, and bold, blinking, reverse video or underlined characters. These highlights are commonly utilized to mark special segments of text or provide indicators of areas into which the user is supposed to insert data. Typically, the video attributes are added to text by inserting "invisible" control commands in text. These commands are not printed on the video screen, only their intended effect is displayed. If the visually impaired person cannot detect the presence of these attributes, he may be unable to recognize important information or respond in the manner intended or, worse yet, he may not be able to understand the text. Thus, a Braille display system must be capable of satisfactorily identifying characters or text possessing video attributes.
In addition, computers have the capability of utilizing several different character sets. For example, besides the U.S. ASCII code there are the U.K. ASCII code and a number of other non-national character sets, as well as line drawing characters and graphics characters. A satisfactory Braille code for use on computers should be capable of identifying each of these for the visually impaired person.
The prior Braille display systems do not adequately address these needs. Either they ignore video attributes and "unusual" characters (e.g. characters from other character sets) or they do an incomplete and poor job of displaying them. The systems which do not simply ignore video attributes or "unusual" text employ one or more of the following three methods to encode text for the Braille display. One method implements a Braille code which has additional dot positions in the multi-dot array. The second method displays the control commands which turn on and off the video attributes within the text. The third method adds one or more prefix symbols to the standard Braille symbol to identify each character having special features and to identify the character set from which the characters are selected. Each of these methods has serious drawbacks.
The codes which utilize more dot positions in the array have greater capacity than the code based upon the 6-dot array but they do not have sufficient capacity to also encode video attributes and identify characters from multiple character sets. All of the expanded array codes basically utilize the same format: a standard 6-dot Braille symbol with one or two modifier dots added in a fourth row. The modifier dots indicate whether the 6-dot symbol is upper case, lower case or a control character. They adopt this format to maintain acceptable compatibility with other existing Braille codes. But because they use this format, these codes usually accommodate only the 128 characters of the ASCII character set. Thus, this approach is inadequate.
Displaying character attribute control commands and character set specifiers along with the text also yields an unsatisfactory solution. Since the highlighted words or phrases are often interspersed throughout the text, this approach leads predictably to very confusing and sometimes unreadable results on the Braille display. First, the normally desired flow of the text is destroyed by the appearance of often complicated control commands on the Braille display. Second, if the reader misses a character set specifier, the text may be unintelligible to the reader. For example, in a mathematical formula utilizing both Greek and Arabic symbols, missing a switch to the Greek character set can completely change the meaning of the formula or make it meaningless.
Another problem is that the systems do not distinguish between visual attribute control commands and other control commands. Thus, line returns, paragraph indents, and other formatting commands will also appear on the Braille display, cluttering up the text and greatly complicating the reading task for the visually impaired person. Moreover, the presence of the control commands on the Braille display disrupts the intended formatting of the text by altering the relative spatial relationship of characters within the text. Where the video screen requires only one position to describe a character along with its video attributes, the Braille display requires several. Thus data which appears in columns on the video screen, will be completely misaligned on a Braille display system that signals the presence of video attributes by displaying the control commands. In instances when preserving vertical alignment of text is especially important, such as in financial reports or balance sheets, the text appearing on the Braille display may become completely undecipherable.
For similar reasons, the third method of adding prefix symbols to standard Braille symbols is equally unsatisfactory. As just noted, using two or more Braille symbols to represent a single character of video displayed text alters the relative spatial relationship of the characters in the text. When "seeing" a properly formatted display is essential to understanding the text, this alteration is unacceptable.
One objective of this invention is to provide a Braille display system which implements a Braille code having sufficient capacity to encode the range of characters and symbols utilized in text created for video display.
Another objective of this invention is to provide a Braille display system which displays text in a Braille code and, in the displayed text, preserves the relative spatial relationships of the characters as they would exist on a video screen display of the same text.
Other objects either are stated in the following description or will become evident in view of the description of the succeeding illustrative embodiment.